Immanuel Kant's impact on contemporary analytic and continental philosophy is hard to overestimate. In Anglo-American analytic circles, Kant's Critique of Pure Reason sets the terms for many debates in metaphysics and the philosophy of mind. In addition, much has been written in the last ten years about Kant's most well-known ethical treatise, The Groundwork for the Metaphysics of Morals. In Anglo-American continental circles, Kant's work has been the object of both ridicule and esteem. By any standard, he is a philosopher of the first rank, standing in importance among philosophers of historical importance such as Hegel, Plato, and Aristotle.
Kant's beginnings did not give strong indications of his philosophical genius. He was born in Koenigsberg, East Prussia in 1724 to a modest family, and he remained in Koenigsberg for his entire life. Kant was never married, nor did he have children. His rather solitary life was only interrupted in its final chapter, when he began publishing his most important work.
His life's final chapter began late. After obtaining a Ph.D. in Philosophy at the University of Koenigsberg at the age of thirty-one, Kant seems to have gone into a long hibernation. The first inklings of professional promise came with The Only Possible Ground of Proof for a Demonstration of God's Existence in 1763, published when Kant was thirty-nine years old. Kant had also studied Latin literature, mathematics, and physics at the University of Koenigsberg, and his wide interests would later prove invaluable for the development of his understanding of metaphysics and epistemology.
Kant obtained a full-time university post at the University of Koenigsberg in 1770. The Critique of Pure Reason was published in 1781, when Kant was fifty-seven years old. The first review it received was unremittingly critical. The (simplified) argument of the Critique is that while empirical objects, like books and chairs, are in some sense very real, they might not be transcendentally real. Chairs are real insofar as they are objects that have to conform to our concepts, to our perceptual categories. But we cannot be sure that they are transcendentally real, because to be sure of this we would ourselves have to transcend our own perceptual limitations to confirm the "transcendental" existence of objects.
This clever argument promised to solve a number of problems that had plagued philosophers for generations. Kant thought it solved, once and for all, questions about God's existence. He claimed that we should no longer attempt, as he himself had done as a young scholar, to prove God's existence. Such attempts are a waste of time, because our concepts only work properly in the empirical world. Since God is, by definition, a spirit, a non-empirical entity, we will never be able to use our limited concepts to prove his (or her) existence. Secondly, Kant's work dispels the urgency of questions about which objects in the world are really, truly real. Real objects, on Kant's view, are simply the ones that are subject to our perceptual categories. We cannot be sure that other, non-empirical objects do not exist, but this should not worry us. After all, we can rest assured that medium-sized objects—houses, boats, and the like—are indeed real. This argument is quite inventive, and to this day it puzzles the sharpest professional philosophers.
The important thing to note about Religion within the Boundaries of Mere Reason is that like the Critique, it represents an ingenious attempt to address a tough philosophical problem concerning the nature of faith and religious obligation. In the Critique Kant employs his own brand of common sense and asks us to set aside questions that we have no chance of adequately answering. We have no need to ask about non-natural entities like God, in other words, since we cannot answer our own questions. Twelve years later, in Religion within the Boundaries of Mere Reason, Kant again encourages us to give up things we don't need. This time, he asks us not to give up questions about God, but rather to give up religious practices that are unnecessary for true moral conduct.
So far we have seen that Kant is fond of asking people to give up things. Sometimes those things are beliefs, and sometimes those things are practices. Enlightenment rationalism (EM) is the broad intellectual movement that Kant is usually identified with, though Kant's work differs from the work of other representatives of this movement. Historians usually say that Enlightenment rationalism begins in the mid- to late-seventeenth century and ends in the early nineteenth century. Most representatives of this movement believed that human beings (a) deserve more freedom than they actually enjoy, (b) are bestowed with reason, an ability that tracks the good through trial and error, and (c) should therefore not be subject to monarchical, tyrannical political and social institutions.
Unfortunately, people describing the beliefs of Enlightenment philosophers often bundle these distinct claims under one single idea, namely that human reason is unqualifiedly good and by itself would destroy evil political institutions and wayward beliefs. This false summary is extremely misleading at best, because most Enlightenment philosophers had reservations about reason. They did not, as this summary suggests, believe that reason was an unqualified good. Let us take a closer look at how Kant himself interpreted the three distinct elements of Enlightenment thought.
Kant believes that human beings deserve to be as free as possible. And he believes that freedom comes in at least two flavors, both of which human beings have a right to enjoy. First, we should have the right to live without political or social institutions that rob people of freedoms. In cases where giving up freedom has a larger, justifiable purpose, Kant has no complaints. Justifiable purposes may include ensuring public safety, protecting personal property, and providing public subsidies for the less fortunate. But when governments rob people of liberty for reasons that are not justifiable to citizens themselves, then there is a problem. The idea that governments must answer to their citizens is both a foundational element of real democracy and the subject of a lot of interesting work in democratic theory.
Secondly, people must be free of coercive influences when making their own private choices. Political institutions, therefore, are not the only obstacles to freedom. Friends, relatives, spouses, and social institutions sometimes coerce us into doing things we would otherwise avoid. Of course, children sometimes need to be coerced, so that they can avoid getting into trouble, a point of which Kant is aware. But the situation for rational adults of sound mind is different. In Kant's view, reasonable adults can undoubtedly know what morality requires without relying on the coercive "wisdom" of a particular church. With this belief, Kant robs the church of its claim to fame, that is, the idea that the church has the last word on moral questions. Kant's general objective in the Religion is to free individuals from religious traditions that interfere with the individuals' ability to adopt the right moral principles.
Let us move on to the second element of Enlightenment thought, which is the idea that all human beings are bestowed with reason, reason that helps us, through trial and error, figure out what is good. To a certain extent, Kant does believe that reason can help human beings analyze social and political problems of all sorts. He also believes, as most Enlightenment thinkers do, that reason can help organize society in accordance with what justice requires. However, Kant does not believe that unaided reason naturally gravitates to the good. In fact, the Critique of Pure Reason was written to reveal just how far off track reason naturally travels when left to its own devices. While reason can be a helpful tool, it must be properly controlled so that we do not unreflectively accept religious doctrines for which we have no evidence. That proper control comes from what Kant calls the critical method. Basically, the critical method is a philosophical approach that allows people to discover which questions reason can answer, and which ones it cannot. So, while Kant does believe that reason can help us supplant unjust political regimes with better ones, he does not believe that reason is an unqualified good. Rather, he believes, we must employ reason critically in order to avoid heading down the wrong path.
As for the third element of Enlightenment thought, Kant believes that human beings are not meant to live under tyrannical political regimes. Because these regimes curb our freedom, he says, they should be supplanted by democratic regimes which respect political liberties. But Kant has a deeper explanation of why human beings are actually more fit for democratic institutions than they are for other kinds of political regimes. He insists that the appeal of democratic institutions cannot simply be explained by the fact that we possess reason. In his view, as rational creatures we are destined to promote "the highest good as a good common to all" (6:97). Democratic political institutions appeal to us partly because they facilitate the pursuit of common goals. Unlike some other Enlightenment thinkers, Kant holds that democracy is not only humane, but also in keeping with the basic human desire to pursue collective ends.
The Enlightenment is a very complex movement, and it is large enough to allow for a wide range of views on its main tenets. It is important to remember that Kant is a critical representative of the Enlightenment. He regards reason as a tool that human beings have at their disposal, a tool they can choose to use wisely or poorly. In Religion within the Boundaries of Mere Reason, Kant encourages us to use this powerful tool wisely, for doing so is the only way to commit ourselves firmly to an enlightened, moral religion.